Optical Interferometric System Research Articles

Broadband Waveguide Chip Design with Phase Measurement Function for Enhancing Optical Interferometric Imaging

The waveguide chip with a phase measurement function has garnered significant attention in the field of imaging optics, emerging as a crucial component in optical interferometric imaging systems. Enhancing the working bandwidth of these waveguide chips is essential for improving the imaging quality of interferometric systems. However, most existing designs primarily focus on narrow bands, with no reported research on broadband designs. This paper introduces a novel broadband waveguide chip design that incorporates a phase measurement function. We explore the fundamental structure and working principle of this innovative design. Fabricated on a silicon substrate, the chip features a silicon dioxide cladding layer and a germanium-doped silicon dioxide core layer, strategically optimized for performance. Utilizing the Beam Propagation Method (BPM), we conduct detailed simulations to determine the optimal device parameters. The simulation results demonstrate the effectiveness of our design, showing a phase measurement deviation of approximately 5° at a center wavelength of 1550 nm across a 300 nm wavelength range. The loss of the device is approximately 0.8 dB. These findings provide a solid foundation for future experimental implementations and fabrications, offering both a theoretical framework and technical reference for advancing the practical use of broadband waveguide chips with phase measurement functions in optical interferometric imaging.

Resolving the Refractive Indices of Transparent and Translucent Liquids from the Spacings, Spatial Frequencies, and Directions of Interference Fringes

In this work, we present a novel approach to resolve the refractive indices of transparent and translucent liquids from straight interference fringes. The optical path difference between the two arms of the Mach–Zehnder interferometer is first derived by assuming a reference plane wave interfering with a plane wave passing through a rectangular cuvette. The analytic expressions for the liquid refractive indices are then deduced, describing how the refractive index is related to the fringe spacings, spatial frequencies, and directions. The structure coefficients in the above formulas are determined from the fringe spacings and directions of the interference patterns of the empty cuvette and the cuvette filled with a liquid of a known refractive index. The NaCl solution and Coca Cola are adopted as the test examples to show experimentally the validity of the proposed method. There is good agreement between the refractive indices obtained from the fringe spacings and direction of a single interference pattern. The sensitivity and resolution of this method are dependent on the structure of the experimental systems and thus can be adjusted in a controlled manner. The proposed method is simple to implement and can be easily extended to other high precision optical interferometer systems.

Study on Dual-Wavelength Wide-Spectrum Erbium-Doped Fiber Ring Laser for Optical Fiber Interferometric Sensing System

In this paper, a novel dual-wavelength wide-spectrum erbium-doped fiber ring laser (EDFRL) for optical fiber sensing system is proposed and experimentally demonstrated. The output of EDFRL is theoretically simulated and classified depending on the theoretical analysis of laser threshold condition into “excited state” and “nonexcited state”. The influence of pump wavelength, fiber laser configuration, EDF length and output coupling ratio of EDFRL is discussed. The EDFRL pumped at 1480 nm wavelength and backward-pumped mode could achieve the stable maximum wide-spectrum output power. The output power fluctuation is lower than 0.06 dB and the center wavelengths shift is less than 0.01 nm. The practicability of EDFRL in a hybrid M-Z and Sagnac interferometer optical fiber sensing system is demonstrated through the comparison of SLD and EDFRL. Consequently, the EDFRL proposed in this study is expected to replace the traditional SLD in the optical fiber interferometric sensing system at a lower cost.

A New Optical Interferometric Biosensing System Enhanced with Nanoparticles for Alzheimer's Disease in Serum.

In this scientific work, we demonstrate, for the first time, a new biosensing system and procedure to measure specifically the total Tau (T-Tau) protein in serum, one of the most relevant biomarkers of Alzheimer's disease (AD). AD is a progressive brain disorder that produces neuronal and cognitive dysfunction and affects a high percentage of people worldwide. For this reason, diagnosing AD at the earliest possible stage involves improving diagnostic systems. We report on the use of interferometric bio-transducers integrated with 65 microwells forming diagnostic KITs read-out by using the Interferometric Optical Detection Method (IODM). Moreover, biofunctionalized silicon dioxide (SiO2) nanoparticles (NPs) acting as interferometric enhancers of the bio-transducers signal allow for the improvement of both the optical read-out signal and its ability to work with less-invasive biological samples such as serum instead of cerebrospinal fluid (CSF). As a result, in this paper, we describe for the first time a relevant diagnostic alternative to detect Tau protein at demanding concentrations of 10 pg/mL or even better, opening the opportunity to be used for detecting other relevant AD-related biomarkers in serum, such as β-amyloid and phosphorylated Tau (P-Tau), neurofilaments, among others that can be considered relevant for AD.

Characterization of Mass Transfer within the Crystal-Solution Boundary Layer of l-Alanine {120} Faces Using Laser Interferometry during Growth and Dissolution.

Crystallization and dissolution are important processes to consider in drug development as well as many other industrial processes. Many current growth and dissolution models are based on bulk solution properties and do not implicitly consider concentration variation close to the crystal surface-solution interface and how this is mediated by solute diffusive mass transfer. Solution boundary layer thickness and concentration distribution, for the {120} crystal habit face of single crystals of l-alanine in saturated aqueous solutions during both growth and dissolution processes, is measured as a function of super/undersaturation using a Mach-Zehnder optical interferometer system. Further analysis allows determination of the diffusion coefficient and mass flux within the boundary layer as well as whether the processes are controlled by mass transfer or crystal interfacial kinetics. The measurement of this study revealed that the {120} face was not saturated at its surface during growth or dissolution meaning both processes were somewhat limited by their crystal interfacial kinetics. Growth was limited by crystal interfacial kinetics at all supersaturations to the same degree, whereas dissolution had a mixed dependency on crystal interfacial kinetics and mass transfer at lower undersaturations becoming more limited by mass transfer at higher undersaturations. Boundary layer thickness increased with super/undersaturation but to a lesser degree than the increase in the concentration difference between the crystal surface and bulk solution leading to a higher mass flux of solute molecules through the boundary layer. At the same relative super/undersaturation mass flux of solute molecules was faster during dissolution which was concurrent with its increased surface to bulk solution concentration difference and boundary layer thickness.

Application of a Multiple Regression Model for the Simultaneous Measurement of Refractive Index and Temperature Based on an Interferometric Optical System

Interferometric optical systems have been proposed for implementing dual‐parameter optical sensors. For this type of sensors, the sensitivity matrix equation is generally used to determine the parameters to be measured based on the sensitivity of each parameter to one particular feature of the output reflective spectrum of the interferometric system. One of the disadvantages of this method is that the measurement ranges will be very short if the sensitivities are not linear or if these present cross‐sensitivity. In this work, a multiple regression model for the simultaneous detection of refractive index and temperature based on an interferometric optical sensor is proposed. Here, the mathematical model is a weighted sum of features used to estimate the values of two response variables. These features are functions of an initial set of 27 explanatory variables whose values were extracted of the output reflective spectrum of the interferometric system. Besides, in order to sustenance the model application, the sensor was modeled and experimentally carried out. Three cases were studied: the estimation of temperature at different refractive indices, the estimation of temperature when refractive index is equal to one, and the estimation of refractive index at different temperatures. For each one of these cases, an optimal basis of functions was founded with the algorithm proposed and used to estimate the values of the response variables. Besides, a technique to reduce the initial set of variables was implemented. Finally, for the experimental data, For each one of these cases, an optimal basis of functions was founded with the algorithm 1 proposed and used to estimate the values of the response variables.

Интерференционный метод контроля выпуклых гиперболических поверхностей с использованием дифракционного оптического элемента

Interference control methods are making it possible to evaluate with high accuracy errors in the shape of the optical part surface profile. The interference pattern processing allows obtaining a map of the surface deviations at each of its points with an accuracy of half the wavelength. An interference method is proposed for testing the convex hyperbolic surfaces, which could be introduced to control mirrors with large aperture angles in the imaginary geometric focus. The proposed auto-collimation control scheme consists of a helium-neon laser with the wavelength of 632.8 nm, a meniscus lens and a planar axisymmetric diffractive optical element to correct the meniscus spherical aberration. Numerical method is presented for calculating the optical diffraction element using a phase profile on the example of the secondary hyperbolic mirror of the Millimetron space telescope. The developed scheme was simulated in the Zemax OpticStudio program. The approximation error of the calculated phase profile was evaluated depending on the number of phase coefficients. The Fizeau interferometer optical system is proposed to implement the developed method. The influence of errors in installing a controlled mirror on the interference pattern for axial displacement, transverse displacement and tilt was determined. The residual wave aberration was evaluated in the control system

A modified Michelson interferometer to measure sub-milliradian changes in angle

Modern short-range gravity experiments that seek to test the Newtonian inverse-square law or weak equivalence principle of general relativity typically involve measuring the minute variations in the twist angle of a torsion pendulum. Motivated by various theoretical arguments, recent efforts largely focus on measurements with test mass separations in the sub-millimeter regime. To measure the twist, many experiments employ an optical autocollimator with a noise performance of ∼300 nrad/Hz in the 0.1–10 mHz band, enabling a measurement uncertainty of a few nanoradians in a typical integration time. We investigated an alternative method for measuring a small twist angle through the construction of a modified Michelson interferometer. The main modification is the introduction of two additional arms that allow for improved angular alignment. A series of detectors and LabView software routines were developed to determine the orientation of a mirror attached to a sinusoidally driven rotation stage that oscillated with an amplitude of 0.35 mrad and a period of 200 s. In these measurements, the resolution of the interferometer is 8.1 μrad per fringe, while its dynamic range spanned 0.962 mrad. We compare the performance of this interferometric optical system to existing autocollimator-based methods, discussing its implementation, possible advantages, and future potential, as well as disadvantages and limitations.

Temperature dependence of the thermo-optic coefficient in 4H-SiC and GaN slabs at the wavelength of 1550\xa0nm

The refractive index and its variation with temperature, i.e. the thermo-optic coefficient, are basic optical parameters for all those semiconductors that are used in the fabrication of linear and non-linear opto-electronic devices and systems. Recently, 4H single-crystal silicon carbide (4H-SiC) and gallium nitride (GaN) have emerged as excellent building materials for high power and high-temperature electronics, and wide parallel applications in photonics can be consequently forecasted in the near future, in particular in the infrared telecommunication band of λ = 1500–1600 nm. In this paper, the thermo-optic coefficient (dn/dT) is experimentally measured in 4H-SiC and GaN substrates, from room temperature to 480 K, at the wavelength of 1550 nm. Specifically, the substrates, forming natural Fabry–Perot etalons, are exploited within a simple hybrid fiber free-space optical interferometric system to take accurate measurements of the transmitted optical power in the said temperature range. It is found that, for both semiconductors, dn/dT is itself remarkably temperature-dependent, in particular quadratically for GaN and almost linearly for 4H-SiC.

Shallow seafloor seismic wave monitoring using 3-component fiber optic interferometric accelerometer

A fiber optic interferometric seismic monitoring system developed by us was deployed on the shallow seafloor near the Wuchang oceanic monitoring station off the Hainan Island, in the South China Sea, in 2017. In the past three plus years, it has recorded more than 40 teleseismic activities of magnitude 6.0+. We analyze these shallow seafloor observed seismic signals monitored by the fiber optic interferometric three-component accelerometer from the perspective of analyzing the underwater ambient seismic noise and the attenuation of the noise in the shallow seafloor seismic signals. The ambient seismic noise produced by wind, wave, shipping, and on-shore manmade activities admixed in the seismic signal is analyzed and discussed in detail. And the attenuation of such noise in the shallow seafloor seismic data using a hybrid denoising algorithm is demonstrated by applying it to three representative seismic events having different distances and magnitudes, with results showing that the noise in the shallow seafloor seismic signal is effectively reduced, and the ratio of the maximum acceleration value of seismic wave to the noise level is improved by more than 32 dB, rendering the seismic waves clearly observable.

Optical and Electrical Properties of the films of ALTiO2 prepared by Magnetron Sputtering

In the present work, ALTiO2 thin films were deposit On a glass substrate by using a DC magnetron sputtering at varying currents (170,180,200) mA. The thickness of ALTiO2 thin films was calculated using an optical interferometer system that used a He-Ne laser with a wavelength λ of (632.8)nm. The thickness of the thin films was (340,162,129) nm. UV-Vis spectroscopy was used to investigate optical properties. The wavelength spectrum between (300 -1000)nm was used to record the absorption and transmittance spectra of ALTiO2 thin films. With increasing thickness and currents, the optical band gap decreases from (3.2 to 1.9) ev. The electrical properties indicate that as the ALTiO2 film thickness increases (340,162,129) nm respectively (1.19 to 9.84) the resistivity decreases

THE EFFECTIVE COHERENCE LENGTH DEFINITION IN PARTIALLY COHERENT LIGHT INTERFEROMETER

The influence of numerical aperture of the Linnik interferometer optical system on the interferogram contrast was investigated. It was shown that the numerical aperture growth leads to effective coherence length decreasing. The modeling and full-scale experiments results were presented.

An Interferometric Optical Fiber Perimeter Security System Based on Multi-Domain Feature Fusion and SVM

In this paper, an interferometric optical fiber perimeter security system based on multi-domain feature fusion and support vector machine (SVM) is reported. To improve the intrusion event classification accuracy and reduce the overall cost, advanced optical fiber sensor technique and data analysis method are synthesized to build the system. For the optical component, the Michelson interferometer sensor structure and the rectangular-pulse binary phase modulation method are adopted to reduce the system complexity and cost. For the electronic data analysis component, mixed domains (including time, frequency and wavelet domains) features are selected and the SVM is adopted to classify the intrusion event type. Specifically, the zero-crossing rate (ZCR) is chosen as the feature element in the time domain, whose threshold is determined by analyzing the environmental noise. The variance of the power spectral density (PSD) of the phase signal in four frequency bands are selected as the feature element in the frequency domain. The energy of the phase signal by using the wavelet packet decomposition in four full frequency bands is chosen as the feature element in the wavelet domain. All the acquired features corresponding to various event conditions are combined into the feature vector data set, which are trained and predicted by the SVM. In the field experiment test, the proposed identification scheme was used to identify and classify five kinds of events, including non-intrusion, climbing, shaking, iron bar knocking and fiber cable shearing. The achieved average classification accuracy reached 94.4%.

Compact snapshot dual-mode interferometric system for on-machine measurement

To meet the need of on-machine metrology in optical manufacturing, a compact and snapshot dual-mode interferometric system is proposed for surface shape and roughness measurement. To simplify the measurement process between surface shape and roughness, a novel concept of using optical filters to separate the beam paths in the reference arm is introduced. A pixelated camera with a micro-polarizer array acquires four pi/2 phase-shifted interferograms simultaneously to minimize the environmental disturbance. Besides, the configuration-optimization-based subaperture stitching technique is introduced to extend the measurable aperture range. Both numerical analysis and experiments have been carried out to demonstrate the feasibility of the proposed compact snapshot dual-mode interferometer. The proposed system provides a powerful and portable tool to achieve on-machine surface characterization of various optical elements over a wide range of spatial frequencies and aperture sizes.

Two Correlated Interferometric Optical Fiber Systems Applied to the Mining Activity Recordings

In order to meet new directions of research in the field of rotational seismology, a registration of rotation phenomena from mining seismic shocks was carried out by two interferometric optical systems. Applied instruments are based on the Sagnac effect and measure the rotation rate in a direct way. Systems have a wide measuring range both in the case of signal amplitude as well as frequency range. Allan variance analysis has indicated that they have proper parameters for the rotational seismology investigation (angle random walk equals 3.20 · 10−8 rad/√s, as well as bias instability equals 2.41 · 10−8 rad/s). Moreover, regarding applied special electronic processing, they provide rotation rate as an output instead of a change of an angle like in commercially available fiber optic gyroscopes. The optical head of the constructed systems uses depolarized light in order to avoid polarization effect. Systems are remotely controlled by the Internet and adapted to an independent power supply which makes them fully autonomous. Correlation between data gathered by two systems applied in a geophysical observatory in Ksiąz, Poland, have been calculated according to the person's correlation coefficient.

A bio-inspired sound source localization sensor with internal coupling

The mechanism of using internal coupling to enhance directional hearing has been found in various animals across multiple length scales, including crickets, lizards, frogs, birds, and alligators. For each eardrum, the acoustic stimuli impinge not only on the front side but also on the opposing side via the connecting cavity. The combination of these two stimuli renders a much higher directional sensitivity than the case with two uncoupled independent receivers. Inspired by this mechanism found in Nature, here we present a bio-inspired sound source localization sensor which consists of two pre-tensioned membranes on a three-dimensional printed housing. The vibration of the two membranes is detected by a low coherence fiber optic interferometric system. The experimental results from this prototype will be demonstrated to validate the feasibility of developing miniature bio-inspired devices for sound source localization.

Non-redundant array configurations for optical interferometric systems combined with a large telescope

In this paper, we propose a method to design the configuration of the interferometric array working with a large telescope. It limits the array configuration region and minimum aperture distance to make sure baseline length is in a certain interval. And it gives aperture locations by “push” and “pull” operations. The UV-plane coverage obtained from this method has the advantage that there is no overlap between UV-plane coverage from the interferometric array and the large aperture telescope, and the overall UV-plane coverage is non-redundant and symmetric. Specifically, design results with varying diameters of the large telescope are provided.

Partial Discharge Ultrasound Detection Using the Sagnac Interferometer System.

Partial discharge detection is crucial for electrical cable safety evaluation. The ultrasonic signals frequently generated in the partial discharge process contains important characteristic information. However, traditional ultrasonic transducers are easily subject to strong electromagnetic interference in environments with high voltages and strong magnetic fields. In order to overcome this problem, an optical fiber Sagnac interferometer system is proposed for partial discharge ultrasound detection. Optical fiber sensing and time-frequency analysis of the ultrasonic signals excited by the piezoelectric ultrasonic transducer is realized for the first time. The effective frequency band of the Sagnac interferometer system was up to 175 kHz with the help of a designed 10 kV partial discharge simulator device. Using the cumulative histogram method, the characteristic ultrasonic frequency band of the partial discharges was between 28.9 kHz and 57.6 kHz for this optical fiber partial discharge detection system. This new ultrasound sensor can be used as an ideal ultrasonic source for the intrinsically safe detection of partial discharges in an explosive environment.

Subwavelength optical lithography via classical light: A possible implementation

The resolution of an interferometric optical lithography system is about the half wavelength of the illumination light. We proposed a method based on Doppleron resonance to achieve a resolution beyond half wavelength [Phys. Rev. Lett. 96, 163603 (2006)]. Here, we analyze a possible experimental demonstration of this method in the negatively charged silicon-vacancy (${\mathrm{SiV}}^{\ensuremath{-}}$) system by considering realistic experimental parameters. Our results show that quarter wavelength resolution and beyond can be achieved in this system even in room temperature without using perturbation theory.

Label-free tissue scanner for colorectal cancer screening.

The current practice of surgical pathology relies on external contrast agents to reveal tissue architecture, which is then qualitatively examined by a trained pathologist. The diagnosis is based on the comparison with standardized empirical, qualitative assessments of limited objectivity. We propose an approach to pathology based on interferometric imaging of “unstained” biopsies, which provides unique capabilities for quantitative diagnosis and automation. We developed a label-free tissue scanner based on “quantitative phase imaging,” which maps out optical path length at each point in the field of view and, thus, yields images that are sensitive to the “nanoscale” tissue architecture. Unlike analysis of stained tissue, which is qualitative in nature and affected by color balance, staining strength and imaging conditions, optical path length measurements are intrinsically quantitative, i.e., images can be compared across different instruments and clinical sites. These critical features allow us to automate the diagnosis process. We paired our interferometric optical system with highly parallelized, dedicated software algorithms for data acquisition, allowing us to image at a throughput comparable to that of commercial tissue scanners while maintaining the nanoscale sensitivity to morphology. Based on the measured phase information, we implemented software tools for autofocusing during imaging, as well as image archiving and data access. To illustrate the potential of our technology for large volume pathology screening, we established an “intrinsic marker” for colorectal disease that detects tissue with dysplasia or colorectal cancer and flags specific areas for further examination, potentially improving the efficiency of existing pathology workflows.